Shares of CSX fell about 5 per cent after Buffett told CNBC he was not interested in a merger, dousing investor hopes that Berkshire’s rail unit BNSF would acquire the rival railroad operator. A representative for Berkshire later confirmed Buffett’s remarks.

CSX ( NASDAQ: CSX) remains open to an approach from Warren Buffett's ( NYSE: BRK.B) BNSF, but no offer has been made, according to CNBC's David Faber on Monday. There "have not been any talks of any kind involving an actual acquisition," Faber said on the business network. "They haven't been approached. They haven't gotten an offer at CSX."

Buffett met CSX CEO Joe Hinrichs on Aug. 3 to discuss more cooperation between the railroads, which are establishing routes linking Charlotte and Jacksonville to Southern California.